RFID-transponders, sometimes referred to as RFID-tags (RFID=Radio Frequency Identification) are widely used for recognizing persons and objects.
An RFID-transponder may be devised as a small tag and carries stored information, such as an identity number, identifying an object or a person. In order to retrieve the stored information an interrogating apparatus is used. The apparatus emits an interrogating radio signal or field, which causes the RFID-transponder to reply with a signal, comprising the stored information. The interrogating apparatus may then receive the reply signal.
Such RFID transponders are used for instance in connection with access control or as an alternative to bar-codes. In other common applications RFID transponders are used in car immobilisers and for identifying domestic animals.
It has been suggested to provide portable, electronic devices, such as mobile phones, with RFID transponders. This enables additional functionalities in connection with such devices. For instance, a mobile phone may then be used also as an access control card. Such functionalities often need strong security.
A problem with using such devices in this manner is that they are sometimes stolen, lost, sold or given away. Any access right or user registration given to the associated RFID transponder identity is then inherited by the new possessor of the device. This implies a lack of security, since the device may be misused, and makes portable, electronic devices with RFID-transponders less credible.